Fix Instruction.repeat with conditionals
#11940
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We can't put register conditionals within an `Instruction.definition` field; the data model of `QuantumCircuit` doesn't permit closing over registers from within definitions. This commit moves a condition to the outer `Instruction` that's returned.
jakelishman
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Pull Request Test Coverage Report for Build 8171222509Warning: This coverage report may be inaccurate.This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.
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releasenotes/notes/fix-instruction-repeat-conditional-dfe4d7ced54a7bb6.yaml
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Co-authored-by: Luciano Bello <bel@zurich.ibm.com>
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I've also updated the documentation of |
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* Fix `Instruction.repeat` with conditionals We can't put register conditionals within an `Instruction.definition` field; the data model of `QuantumCircuit` doesn't permit closing over registers from within definitions. This commit moves a condition to the outer `Instruction` that's returned. * Avoid 'to_mutable' if not needed * Add proviso on repeated conditionals in documentation * Update wording in release note Co-authored-by: Luciano Bello <bel@zurich.ibm.com> --------- Co-authored-by: Luciano Bello <bel@zurich.ibm.com>
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* Fix `Instruction.repeat` with conditionals We can't put register conditionals within an `Instruction.definition` field; the data model of `QuantumCircuit` doesn't permit closing over registers from within definitions. This commit moves a condition to the outer `Instruction` that's returned. * Avoid 'to_mutable' if not needed * Add proviso on repeated conditionals in documentation * Update wording in release note Co-authored-by: Luciano Bello <bel@zurich.ibm.com> --------- Co-authored-by: Luciano Bello <bel@zurich.ibm.com>
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* Fix `Instruction.repeat` with conditionals We can't put register conditionals within an `Instruction.definition` field; the data model of `QuantumCircuit` doesn't permit closing over registers from within definitions. This commit moves a condition to the outer `Instruction` that's returned. * Avoid 'to_mutable' if not needed * Add proviso on repeated conditionals in documentation * Update wording in release note Co-authored-by: Luciano Bello <bel@zurich.ibm.com> --------- Co-authored-by: Luciano Bello <bel@zurich.ibm.com> (cherry picked from commit 6ebb7aa)
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* Fix `Instruction.repeat` with conditionals We can't put register conditionals within an `Instruction.definition` field; the data model of `QuantumCircuit` doesn't permit closing over registers from within definitions. This commit moves a condition to the outer `Instruction` that's returned. * Avoid 'to_mutable' if not needed * Add proviso on repeated conditionals in documentation * Update wording in release note Co-authored-by: Luciano Bello <bel@zurich.ibm.com> --------- Co-authored-by: Luciano Bello <bel@zurich.ibm.com> (cherry picked from commit 6ebb7aa) Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
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Summary
We can't put register conditionals within an
Instruction.definitionfield; the data model ofQuantumCircuitdoesn't permit closing over registers from within definitions. This commit moves a condition to the outerInstructionthat's returned.Details and comments
Fix #11935
Fix #11936 (though note that #11761 would then be triggered for OQ3).
Important
As implemented, this commit isn't necessarily a completely valid transformation, but I'm putting it up in this form for a bit of discussion.
The point is that an instruction can in theory affect its own condition; consider a
Measure().c_if(cr, value), where the measure instruction within the circuit is applied to a clbit that's incr. To go further, consider the custom instruction whose definition ish q[0]; measure q[0] -> c[0];- this is clearly not idempotent under ac-based condition (one could argue that the baremeasurewas, in the context of a noiseless abstract circuit, since the first measure would collapse the state).Given that
Instruction.repeatis only applied without a circuit context, and we're moving to removeInstruction.conditionfor these same sorts of reasons (in favour ofIfElseOp), I think this is a transformation we can accept, though perhaps with additional documentation.